1. Field of the Invention
The present invention relates to a method for modifying at least one calculation algorithm in a biopsy system, the calculation algorithm having an influence on the determination of the position of a cell or tissue-sampling area in a stereotactic biopsy procedure.
2. Description of the Prior Art
The present invention also relates to a stereotactic biopsy system for examining the breast, the female breast in particular, of the type having a mammography apparatus, a biopsy apparatus and a calculation unit for stereotactic calculation of the position of a cell or tissue-sampling area.
Swedish Patent Application, SE-8306243-0, discloses a method for locating the position of a three-dimensional point in an object, e.g. a female breast, in conjunction with x-ray irradiation of that object. This is achieved by fixing the object in a predefined position, whereupon it is exposed with an exposure apparatus from two angles on either side of a center line perpendicular to the image plane, so that a first image and a second image are obtained. The two-dimensional position of the sought point in the two images is then determined in relation to an index in each of the images. The coordinates of the point in relation to the index are processed to obtain control signals for setting an aiming instrument, with an insertion instrument, to the desired point in the object.
U.S. Pat. No. 5,240,011 discloses a motor-driven unit for use in a biopsy system for automatic positioning of a biopsy needle in order to allow insertion of the needle to a previously identified point of interest in the breast of a patient.
Even though most contemporary stereotactic mammographic biopsies are made using film, systems incorporating digital image detectors have been introduced for mammography in recent years.
Extreme accuracy is required in all types of stereotactic biopsies in determining the x, y, z coordinates of a cell or tissue-sampling area in which a suspected tumor or some other tissue change has been discovered. The physician needs to be absolutely certain that a specimen has been taken from the interesting (suspicious) area. Locations are determined with a calculation algorithm which includes e.g. the apparatus constants of the system. If this very high degree of accuracy is to be achieved, very exact values for apparatus constants must be used, which truly correspond to system realities. Examples of apparatus constants are the x-ray tube's angle of inclination, the x-ray focus-detector distance, the distance to the axis of rotation, the table top-to-focus distance and the table top-to-detector distance.
Installation of a stereotactic biopsy unit is often a very time-consuming and patience-demanding procedure, since calibration of the tube's angle of inclination (an apparatus constant) is often necessary. Calibration is also performed during the manufacture and service of systems, especially when usage-induced wear can affect the apparatus constants which have been previously set.